I can't understand how below code snippet works. Especially std::initializer_list usage.
template<typename ... T>
auto sum(T ... t)
{
typename std::common_type<T...>::type result{};
std::initializer_list<int>{ (result += t, 0) ... };
return result;
}
template<typename ... T>
auto sum(T ... t)
{
//getting the common type of the args in t and initialize a new var
//called result using default constructor
typename std::common_type<T...>::type result{};
//(result += t, 0) ... this just sum the result and the next arg in the
//parameter pack and then returns zero, hence the initializer_list will be filled
//only by zeros and at the end result will hold the sum of the args
std::initializer_list<int>{ (result += t, 0) ... };
return result;
}
It's equivalent to
template<typename ... T>
auto sum(T ... t)
{
return (t+...);
}
(result += t, 0) ... returns 0,0,0,.. inside the parenthesis. like if you write {0,0,0,...}result += t. And also, compiler doesnt care this parameter. If I changed it(result += t, 2 or result += t, false), result remains same. And If I delete this param, result remains same again, but compiler gives warning.